Hydrogels are used in biomedical applications, such as drug delivery vehicles, cell encapsulation matrices, and tissue engineering scaffolds because many of their physical properties are similar to natural tissue. Hydrogels are insoluble 3-D networks of physically or chemically cross-linked hydrophilic polymers, which exhibit a high degree of swelling in aqueous environments.
Alginate is a linear unbranched polysaccharide derived from seaweed that contains the repeating units of 1,4-linked β-D-mannuronic acid and α-L-guluronic acid. Alginates have reversible gelling properties in aqueous solutions related to the ionic interactions between divalent cations. Alginate can be formed into a hydrogel and used as a drug delivery vehicle.
There is limited control over the mechanical properties, swelling ratios, and degradation profiles of ionically cross-linked alginate hydrogels, which is likely due to the uncontrollable loss of divalent cations into the surrounding environment. Approaches to chemically crosslinking alginate microcapsules or macroscopic hydrogels may utilize intermolecular covalent cross-linking rather than ionic cross-linking in order to synthesize alginate hydrogels with a wide range of mechanical properties. However, the reagents and reaction conditions used with such approaches can be toxic to encapsulated cells or growth factors, and hydrogels covalently cross-linked are not biodegradable.